Equilibrium

Equilibrium is the condition of a system in which competing influences are balanced. The word may refer to:

Science

Biology

• Equilibrioception, the sense of a balance present in human beings and other animals
• Equilibrium unfolding, the process of unfolding a protein or RNA molecule by gradually changing its environment
• Genetic equilibrium, theoretical state in which a population is not evolving
• Homeostasis, the ability of an open system, especially living organisms, to regulate its internal environment
• Punctuated equilibrium, theory in evolutionary biology
• Sedimentation equilibrium, analytical ultracentrifugation method for measuring protein molecular masses in solution
• Equilibrium Theory (Island biogeography), MacArthur-Wilson theory explaining biodiversity character of ecological islands

Physics

• Equilibrium figures of Earth and planets (physical geodesy)
• Equilibrium mode distribution, the state of fiber optic or waveguide transmission in which the propagation mode does not vary with distance along the fiber or changes in the launch mode
• Hydrostatic equilibrium, the state of a system in which compression due to gravity is balanced by a pressure gradient force
• Hyperbolic equilibrium point, a mathematical concept in physics
• Mechanical equilibrium, the state in which the sum of the forces, and torque, on each particle of the system is zero
• Radiative equilibrium, the state where the energy radiated is balanced by the energy absorbed
• Secular equilibrium, a state of radioactive elements in which the production rate of a daughter nucleus is balanced by its own decay rate
• Thermal equilibrium, a state where an object and its surroundings cease to exchange energy in the form of heat, i.e. they are at the same temperature.

Chemistry

• Chemical equilibrium, the state in which the concentrations of the reactants and products have no net change over time
• Diffusion equilibrium, when the concentrations of the diffusing substance in the two compartments are equal
• Donnan equilibrium, the distribution of ion species between two ionic solutions separated by a semipermeable membrane or boundary
• Dynamic equilibrium, the state in which two reversible processes occur at the same rate
• Equilibrium constant, a quantity characterizing a chemical equilibrium in a chemical reaction
• Partition equilibrium, a type of chromatography that is typically used in GC
• Quasistatic equilibrium, the quasi-balanced state of a thermodynamic system near to equilibrium in some sense or degree
• Schlenk equilibrium, a chemical equilibrium named after its discoverer Wilhelm Schlenk taking place in solutions of Grignard reagents
• Solubility equilibrium, any chemical equilibrium between solid and dissolved states of a compound at saturation
• Thermodynamic equilibrium, the state of a thermodynamic system which is in thermal, mechanical, and chemical equilibrium
• Vapor-liquid equilibrium, where the rates of condensation and vapourization of a material are equal

Other

• Social equilibrium, a system in which there is a dynamic working balance among its interdependent parts
• Equilibration, the means of cognitive development in Jean Piaget's cognitive developmental theory

Economics

• Competitive equilibrium, economic equilibrium when all buyers and sellers are small relative to the market
• Economic equilibrium, a condition in economics
• Equilibrium price, the price at which quantity supplied equals quantity demanded
• General equilibrium theory, a branch of theoretical microeconomics
• Intertemporal equilibrium, an equilibrium concept over time
• Lindahl equilibrium, a method proposed by Erik Lindahl for financing public goods
• Partial equilibrium, the equilibrium price and quantity which come from the cross of supply and demand in a competitive market.
• Radner equilibrium, an economic concept defined by economist Roy Radner in the context of general equilibrium
• Recursive competitive equilibrium, an economic equilibrium concept associated with a dynamic program
• Static equilibrium (economics), the intersection of supply and demand in any market
• Sunspot equilibrium, an economic equilibrium in which nonfundamental factors affect prices or quantities
• Underemployment equilibrium, a situation in Keynesian economics with a persistent shortfall relative to full employment and potential output

Game theory

• Correlated equilibrium, a solution concept in game theory that is more general than the well-known Nash equilibrium
• Nash equilibrium, a solution concept in game theory involving two or more players
  • Quasi-perfect equilibrium, a refinement of Nash Equilibrium for extensive form games due to Eric van Damme
  • Sequential equilibrium, a refinement of Nash Equilibrium for extensive form games due to David M. Kreps and Robert Wilson
• Symmetric equilibrium, in game theory, an equilibrium where all players use the same strategy
• Trembling hand perfect equilibrium assumes that the players, through a "slip of the hand" or tremble, may choose unintended strategies
  • Proper equilibrium due to Roger B. Myerson, where costly trembles are made with smaller probabilities

Film and television

• Equilibrium (film), a 2002 science-fiction film
• Equilibrium, alternate title of the 1953 film The Story of Three Loves
  • title of one of the three segments of the film
• "Equilibrium" (seaQuest 2032 episode), episode of seaQuest 2032
• "Equilibrium" (DS9 episode), an episode of Star Trek: Deep Space Nine

Music

• Equilibrium (band), a folk metal band from Germany
• Equilibrium (Fergie Frederiksen album), released in 1999
• Equilibrium (Crowbar album), released in 2003
• Equilibrium (Erik Mongrain album), released in 2008
• IX Equilibrium, an album by the Norwegian band Emperor

Other

• Equilibrium (puzzle), a 3D interlocking type puzzle
• Equilibrium moisture content, the moisture content at which the wood is neither gaining nor losing moisture
• Equilibrium point, node in mathematics
• Reflective equilibrium, the state of balance or coherence among a set of beliefs arrived at by a process of deliberative mutual adjustment

See also

• Balance (ability)
• Disequilibrium (disambiguation)
• Equilibristics, e.g. juggling
• Stability (disambiguation)
• Steady state (disambiguation)